1. Field of the Invention
The present invention relates to a photoresist composition. It also relates to a method of forming a photoresist pattern using the photoresist composition.
2. Description of the Related Art
Semiconductor devices are highly integrated and operate at a high speed. They have been required to form a very fine pattern having a line width which is no more than about 0.5 μm. Conventionally, a photolithography process using a photo-resistive material such as photoresist is typically utilized in forming a pattern for a semiconductor device he photolithography process generally includes a photoresist coating process, an aligning process, an exposing process and a developing process.
The molecular structure of the photoresist, which is changed by light irradiated thereto is coated on the substrate such as a silicon wafer. This forms a photoresist film on the substrate by the photoresist coating process. Then, a photo mask on which an electronic circuit pattern is formed is arranged over the wafer on which the photoresist film is formed during the aligning process. Then, an illuminating light which has a particular wavelength to which the photoresist film is particularly sensitive can be provided. In this way, photo chemical reactions will be incurred when illuminating light is irradiated onto the photo mask. Accordingly, a predetermined electronic circuit pattern can be transcribed onto the photoresist film by the aligning and exposing process. The molecular structures of the photoresist film are selectively changed in accordance with the predetermined electronic circuit pattern. The developing process selectively removes the photoresist film having the changed molecular structures to thereby forming a photoresist pattern on the substrate.
A minimal line width of the photoresist pattern or the semiconductor pattern is determined in accordance with a resolution of an exposing system. The resolution of the exposing system is determined by the wavelength of the illuminating light according to a Rayleigh's equation as follows.R=K1λ/NA  (1)
In this Rayleigh's equation, λ denotes a wavelength of the illuminating light of an exposing system, R denotes a resolution limit of an exposing system, K1 denotes a proportional constant of an exposing process, and NA denotes a numerical aperture of a lens of an exposing process. According to the Rayleigh's equation (1), the wavelength λ of the illuminating light and the proportional constant K1 need to be as small as possible, and the numerical aperture of a lens needs to be as large as possible for decreasing the resolution limit of an exposing system. Thus, the higher the resolution of the exposing system, the shorter the wavelength of the illuminating light, and thus the wavelength of the illuminating light needs to be reduced in order to form a fine photoresist pattern. Among the factors of the Rayleigh's equation, the wavelength λ of the illuminating light is most widely utilized for increasing the resolution limit of an exposing system.
In early 1980s, a G-line light having a wavelength of about 436 nm or an I-line light having a wavelength of about 365 nm were exemplarily used as the illuminating light, and the photoresist pattern was formed having a resolution of from about 350 to about 500 nm. Recently, a krypton fluoride (KrF) excimer laser having a wavelength of about 248 nm, or an argon fluoride (ArF) excimer laser having a wavelength of about 193 nm were used as the illuminating light, and a photoresist pattern has been formed having a resolution of about 180 to about 1240 nm. A recent memory device of a few giga-bytes is now possible to be manufactured having the above referenced fine photoresist pattern (as disclosed in Solid State Technology, January, 2000).
The fine photoresist pattern is influenced to a great extent by a wavelength of the illuminating light, and the exposition system including the illuminating light, and the resolution limit of the exposition system. Examples of a photoresist composition are disclosed in the articles entitled “Photoresist Materials and Processes”, McGraw Hill Book Company, New York 1975, and “Semiconductor Lithography, Principles, Practices and Materials”, Plenum Press, New York 1988.
Various factors such as the optical characteristics of a layer to be patterned, the standing wave caused by a thickness variation of a photoresist film, the light reflected from a reflective notch or the diffraction light diffracted from the layer to be patterned, have been widely known to have much effect on the exposing process for forming the super fine photoresist pattern. That is, those factors have much effect on the photoresist pattern to thereby generate various exposing failures such as the change in a critical dimension of the photoresist pattern and the increase of a surface area of the pattern.
In particular, when the KrF laser or the ArF laser is utilized for the illuminating light, the illuminating light has a high transmissivity with respect to a photoresist film on a substrate due to the wavelength and the strong energy of the laser, so that the photoresist pattern formed by using the KrF laser or ArF laser is much more influenced by the above-mentioned factors of the exposing process. That is, the exposing failures are generated more frequently when the photoresist pattern is formed using the KrF or ArF excimer laser.
Various researches have been conducted for solving the problems caused by the factors of the exposing process. For example, Japanese Patent Laid-Open Publication Nos. 1997-73173, 1997-90637 and 1998-161313 disclose photoresist compositions comprising a resin including an alkali-soluble group protected by a pendant alkali-soluble group that is transformed to be soluble by an alkali material, when the alkali-soluble group is dissociated therefrom by an acid.
In addition, Japanese Patent Laid-Open Publication No. 1999-202479 discloses a method of preventing the standing wave generated from a photoresist film using a photoresist material comprising a photo acid generator, a resin having a hydrocarbon structure that is dissolved by a photo acid generated from the photo acid generator which has a high solubility in an alkali developer, and an oligo alkylene glycol dialkyl ether compound.
Further, U.S. Pat. No. 6,200,728 discloses photoresist compositions comprising a photo acid generator mixture for generating various photo acids, having a different acid strength from each other. A fine photoresist pattern having a high resolution is formed on a boron phosphorus silicate glass using the same photoresist compositions.
However, when the ArF excimer laser is utilized for forming a fine photoresist pattern, there is a problem that a profile of the photoresist pattern is not satisfactory in accordance with a layer to be etched using the photoresist pattern, the thickness of the photoresist pattern, and the reduced design rule that is used by the above-disclosed method and photoresist compositions for the photoresist pattern.